International aid agencies have warned that Haitians are dying needlessly amid "utter chaos" in the organisation of relief efforts after last week's devastating ­earthquake. Some have called for the US to take direct control over the rescue ­operation, while others have said the Americans are part of the problem.

A week into the disaster, aid has failed to reach most Haitians amid logistical confusion and disputes over priorities as the population grows ever more desperate.

Médecins sans Frontières says confusion over who is running the relief effort – the US which controls the main airport, or the UN which says it is overseeing distribution – may have led to hundreds of avoidable deaths because it has not been able to get essential supplies in to the country. "The co-ordination ... is not existing or not functioning at this stage," said Benoit Leduc, MSF's operations manager in Port-au-Prince. "I don't really know who is in charge. Between the two systems (the US and the UN) I don't think there is smooth liaison [over] who decides what."

John O'Shea , the head of the Irish medical charity, Goal, echoed the criticism. He said the Haitian earthquake was one of the most difficult disasters his agency had dealt with but at least there were no political obstacles to aid deliveries, as in Burma and Sudan.

"That means there is only one thing stopping a massive and prodigious aid effort being rolled out and that is leadership and co-ordination. You have neither in Haiti at the moment," he said.

"You have the US military doing their thing at the airport. You have the United Nations saying we're in control of food distribution but the United Nations is not taking the pro-active role that they should be taking.

"And you have a Haitian president saying he's in charge and the Americans being politically correct and saying they will work under him. This is all going to lead to a situation of utter chaos. I can't get all my trucks in from the Dominican Republic because I have no guarantee that the people driving them are not going to be macheted to death on the way down. I can't let my doctors and nurses out on the street of Port-au-Prince."

Aid agencies say the US and the UN pay lip service to being under the authority of the Haitian government but President René Préval has little real control.

Préval's role has largely been limited to appealing for assistance and meeting visitors such as the US secretary of state, Hillary Clinton, and the UN's secretary general, Ban Ki-moon. He has yet to visit the refugee camps packed with his ­desperate compatriots.

The Haitian prime minister, Jean-Max Bellerive, told the Washington Post the government was "overwhelmed" by the crisis.

That is widely recognised by aid agencies. O'Shea called on the Americans to take charge of the whole operation.

"Obama has to say: I'm in charge lads. Everybody would row in behind him. Like or lump the Americans, they're people who have the ability to get a job done. Somebody, somewhere has to grab this thing by the balls," he said.

A major US aid agency, which declined to be named for political reasons, said it agreed with O'Shea. "It's quite apparent that the Haitian system can't handle this and I don't think there's a lot of confidence in the UN to provide security. It's clear the Americans are the ones to do this. There are of course political sensitivities but I think we're beyond that at the moment. Look at the reaction of ordinary Haitians. They are welcoming the Americans with open arms," said an official with the agency.

Others were more sceptical, saying the oversight of aid operations belongs with the UN. On Monday, France's cooperation minister, Alain Joyandet, criticised the US by saying that aid efforts were supposed to be about helping Haiti, not "occupying" it.

But there is general agreement that someone needs to take charge.

The US has about 1,000 troops in Haiti and another 2,000 are on their way. There are also 9,000 UN peacekeepers and international police officers in the country.

There has been criticism from some aid agencies of the Americans for giving priority to military flights at the airport while planes carrying relief supplies are unable to land. MSF has had five planes turned back from the airport in recent days, three carrying essential medical supplies and two with expert surgical personnel.

"We lost 48 hours because of these access problems," said Leduc. "Of course it is a small airport, but this is clearly a matter of defining priorities."

Asked how many avoidable deaths had been caused by the delays, he said that hundreds of critical lifesaving operations had been delayed by two days.

"We are talking about septicaemia. The morgues in the hospitals are full," he said.

The World Food Programme said todaythat agreement had been reached that its flights would receive priority landing at Port-au-Prince airport.

Greg Barrow, a WFP spokesman, said the organisation has only been able to distribute with protection from US or UN troops. "We do need security to carry out distributions," he said.

But Barrow said the more immediate obstacle to delivering aid was the logistical difficulty of getting large amounts of food to Haiti because its main airport is small and main port severely damaged. "What we're looking at the moment is opening up as many air, land and sea corridors as possible even to the point of chartering landing vessels and trucks can just drive off on to the beach, a sort of roll-on roll-off mechanism," he said. US officials have made contingency plans to deal with refugees from Haiti although they say there is no sign that a seaborne exodus is imminent.

The homeland security secretary, Janet Napolitano, appealed to Haitians to remain at home.

"Please: If any Haitians are watching, there may be an impulse to leave the island and to come here," she said. "This is a very dangerous crossing. Lives are lost every time people try to make this crossing. Please do not have us divert our necessary rescue and relief efforts that are going into Haiti by trying to leave at this point."

Thousands of Haitians have fled their country and tens of thousands more have been rescued at sea by the US coast guard over the past 20 years.

Bill Clinton, the former president, visited Haiti today in response to a request from Obama for help in fundraising.